1 Samuel 17:38-40,48-50
Then Saul dressed David in his own tunic. He put a coat of armor on him and a bronze helmet on his head. David fastened on his sword over the tunic and tried walking around, because he was not used to them.
“I cannot go in these,” he said to Saul, “because I am not used to them.” So he took them off. Then he took his staff in his hand, chose five smooth stones from the stream, put them in the pouch of his shepherd’s bag and, with his sling in his hand, approached the Philistine.
As the Philistine moved closer to attack him, David ran quickly toward the battle line to meet him. Reaching into his bag and taking out a stone, he slung it and struck the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground.
So David triumphed over the Philistine with a sling and a stone; without a sword in his hand he struck down the Philistine and killed him.
When God calls you to do something, He prepares you for the task.
David didn’t need Saul’s armor, helmet or sword to defeat Goliath. All those “professional tools” just got in his way. What David needed was to be the man God had created him to be and to fight the way God had trained him to fight.
God has called you to do something. I’m not sure what it might be, but I am sure that He’s given you the tools and the experience you need. Quit trying to be someone you’re not and simply do what you know. Let God lead, take up your sling and kill a giant.